refactor(nanoid): replace gonanoid with custom nanoid implementation for ID generation

Signed-off-by: Deluan <deluan@navidrome.org>

utils/nanoid/nanoid.go

@@ -0,0 +1,52 @@
+package nanoid
+
+import (
+	"crypto/rand"
+	"errors"
+	"math"
+)
+
+// Generate returns a cryptographically secure random string of `size` characters
+// drawn from `alphabet`. It uses bitmask with rejection sampling to avoid modulo bias.
+// The alphabet must be non-empty, contain at most 255 characters, and consist only of
+// ASCII characters. Non-ASCII alphabets (e.g., multi-byte UTF-8) are not supported.
+func Generate(alphabet string, size int) (string, error) {
+	if len(alphabet) == 0 || len(alphabet) > 255 {
+		return "", errors.New("alphabet must be non-empty and at most 255 characters")
+	}
+	if size <= 0 {
+		return "", errors.New("size must be a positive integer")
+	}
+
+	mask := getMask(len(alphabet))
+	step := int(math.Ceil(1.6 * float64(mask) * float64(size) / float64(len(alphabet))))
+
+	id := make([]byte, size)
+	bytes := make([]byte, step)
+	for j := 0; ; {
+		if _, err := rand.Read(bytes); err != nil {
+			return "", err
+		}
+		for i := range step {
+			idx := int(bytes[i]) & mask
+			if idx < len(alphabet) {
+				id[j] = alphabet[idx]
+				j++
+				if j == size {
+					return string(id), nil
+				}
+			}
+		}
+	}
+}
+
+// getMask returns the smallest bitmask >= alphabetSize-1.
+func getMask(alphabetSize int) int {
+	for i := 1; i <= 8; i++ {
+		mask := (2 << uint(i)) - 1
+		if mask >= alphabetSize-1 {
+			return mask
+		}
+	}
+	return 0
+}